How To Get Blue BG With 56K Lights and WB?

G

groveChuck

U-matic Member
I have some tech clients I do videos for, and they (and I) like a wash or slash of dark blue or blue/green in the BG.

But shooting with 56K FLOS, how would I get a blue BG, since I'm balanced for blue???

Blue gel over 56K light? Problem is, I use tungsten in the BG.
 
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So let me get this straight, you are putting daylight flos on your subject and you want to use tungsten balanced lights to put blue in the background.... Wow, that is like one of those ancient Chinese proverb riddles from a cheap kung fu movie!... Trying to wrap my head around it, I see putting full CTO on the flos, WB to that, and then a full CTB on the tungsten lights... that would get the color balance right, but is kind of crazy, with the filter factor of the gels. Since the CTO has less of a filter factor (Full CTO lets through more light than full CTB), you might want to put a full and a half CTO on the flos, WB to that, and then put a half CTB (or maybe 3/4 full for bluer light) on the tungsten lights. That would make the Tungstens blue. I would experiment with that and the camera you are using to see how that holds up.

So, HMI's for the background, with CTB on them, is out of the question?
 
Yeah, sounds like quite the Chinese conundrum, right? :undecided

I'm working with what I have, which is flos for a cool key for talent, and tungsten fixtures for the BG- no HMIs.

You're right, one and a half CTOs + half to three quarter CTB = blue BG, but I'd rather not gel the flos and have the light loss.

I could double blue (party) gel the BG, but that would be even more light loss- sigh... I knew this wasn't going to be easy...
 
You could re-tube your key flos to 3200k and use your 5600k lights with gel for the BG. Many times I will use a 1k tungsten fresnel with a heavy blue gel to paint a BG.
 
Interesting, suggestions from David Smith and David Jones... who's next, David Williams? (ha ha).

Can't retube the flos (or use them as BG), they're Rifa softboxes with giant CFLs (92+ CRI), a very soft light. I use 650s for the BG.

And I'd probably lose too much light gelling with CTO, though i'll probably try it as my only option given what I'm working with.

Any other Davids with tips?... :happy:
 
Is there a David Brown out there with a suggestion?

If you don't want to gel the flos, you might want to set camera to tungsten WB, leave the flos without gels, gel the BG lights with CTB, then make the color correction in post (to bring the flos down to white). This would save you from the light loss of gelling the flos.
 
Hmmm... if I WB tungsten, light daylight- it's blue.
Then CC by removing blue, the BG loses its blue, doesn't it... David? :undecided

What sayeth David White? :grin:
 
groveChuck said:
Hmmm... if I WB tungsten, light daylight- it's blue.
Then CC by removing blue, the BG loses its blue, doesn't it... David? :undecided

What sayeth David White? :grin:
Click to expand...

Yeah, you would have to use double blue on the BG lights to keep the blue. That would really cut down on the light output. Without putting any gel on the flos, I don't see how you could do it. Keep in mind. Full CTO cuts the light by 2/3 stop while Full CTB cuts the light by 1&1/2 stops.

Filter factors CTO CTB.jpg
 
Yep, the lower light loss of the CTO gives me hope, though I don't have a sheet large enough for the softbox right now.
I knew CTO cut less light than CTB, but not precisely, so thanks for the chart!
Where's the chart from?
 
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